Method of microbiological control of paper mill processes

ABSTRACT

A PROCESS FOR THE MMICROBIOLOGICAL CONTROL OF PULP SLURRIES IN THE PAPER INDUSTRY WHEREIN PULP SLURRIES LOCATED IN THE WET END PROCESS OF A PAPER MAKING INSTALLATION CAN BE VIRTUALLY STERILIZED BY THE USE OF A WATER SOLUBLE, ANIONIC SURFACTANT, PREFERABLY THE FORMALDEHYDE-CONDENSED NAPHTHALENE SSULFONATES IN CONJUNCTION WITH CHLORINE OR CHLORINE LIBERATING MICROBICIDES SUCH AS, FOR EXAMPLE, CHLORINE DIOXIDE, HYPOCHLOROUS ACID, CHLORINE WATER, CALCIUM HYPOCHLORITE, THE ALKALI METAL HYPOCHLORITES SUCH AS SODIUM HYPOCHLORITE, AND THE LIKE. THE MICROBICIDAL EFFECTIVENESS OBTAINED WITH THE CONJOINT USE OFF SUCH ANOINIC SURFACTANTS AND CHLORINE OR CHLORINE LIBERATING MICROBICIDES IS EQUIVALENT TO THE USE OF GREATLY INCREASED AMOUNTS OF CHLORINE ALONE WHICH INCREASED AMOUNTS OF CHLORINE WOULD BE OTHERWISE OBJECTIONABLE INSOFAR AS ODOR, CORRISION, LOSS OF RETENTION AND FIBER DEGRADATION ARE CONCERNED.

June 18, 1974 B. BENDINER 3,817,828

METHOD'OF MICROBIOLOGICAL CONTROL OF PAPER MILL PROCESSES Filed Sept, 30, 1970 (WHITE WATER) STOCK CHESTS MACHINE CHESTS HEAD BOX 0R VAT PAPER MAKING MACHINE FOURDRINIER, CYLINDER, ETC.

DRYERS,FELT WEBS TREATMENT CYLINDERS, ETC. SIZING, POLISHING FURTHER PROCESSING, CUTTING, STACKING, ETC.

CUSTOMER INVENTOR BERNARD BENDINER ATT'YS.

US. Cl. 162-161 11 Claims ABSTRACT OF THE DISCLOSURE A process for the microbiological control of pulp slurries in the paper industry wherein pulp slurries located in the wet end process of a paper making installation can be virtually sterilized by the use of a water soluble, anionic surfactant, preferably the formaldehyde-condensed naphthalene sulfonates in conjunction with chlorine or chlorine liberating microbicides such as, for example, chlorine dioxide, hypochlorous acid, chlorine water, calcium hypochlorite, the alkali metal hypochlorites such as sodium hypochlorite, and the like. The microbicidal effectiveness obtained with the conjoint use of such anionic surfactants and chlorine or chlorine liberating microbicides is equivalent to the use of greatly increased amounts of chlorine alone which increased amounts of chlorine would be otherwise objectionable insofar as odor, corrosion, loss of retention and fiber degradation are concerned.

BACKGROUND AND DESCRIPTION OF THE INVENTION The present invention generally relates to the microbiological control of pulp slurries in paper making equipment and, more particularly, is directed to a process wherein virtual sterilization of pulp slurries in the wet end of a paper making installation can be achieved, typically, such portions of a paper making installation would include the stock chests, machine chests, head box and sheet forming machines, for example, the Fourdrinier or cylinder machines or their equivalent.

The importance of effective microbiological control of pulp slurries used in paper manufacturing is well known. Ineffective microbiological control can be manifested by the massive accumulation and deposition of microorganisms on the equipment, particularly those portions of the paper making equipment wherein relatively stagnant bodies of pulp slurries which typically contain from approximately one-half percent to six percent, by weight, of solids are contained, for example, the stock chests, machine chests and head box. Also, ineffective microbiological control can manifest itself throughout the wet end process by the deposition of accumulations of microbiological matter with the pulp on the wire of the sheet forming equipment with the result that breaks can occur in the paper while on such wire. In some instances where excessive amounts of microorganisms are encountered, such microorganisms can result in spotting on the finished paper when in the hands of the ultimate customer. Slime accumulation caused by ineffective microbiological control can result in gradual plugging or occluding of the felts, greatly diminishing their drainage efliciency.

Problems of the type set forth above have necessitated the shutdown of paper making equipment and mechanical cleaning, for example with the aid of boilout solutions. These shutdowns and equipment cleaning not only involve expensive labor expenditures, but, more importantly, are costly to a paper making plant since they result in loss of valuable production time on the machine.

The problem of microbiological control of pulp slurries and process water (whitewater) systems associated therewith is particularly complex and ditlicult since substantial United States Patent Patented June 18, 1974 quantities of water are used and the recycling thereof is essential both from economic and pollution control considerations. With bacteria and fungi being continuously replenished by means of raw material, particularly unsterilized pulp, and makeup water, it is not sufiicient for control of the microbiological population to merely start out with clean equipment and with relatively sterile process water. Moreover, as microorganisms develop in the pulp slurries, they generally acquire a protective slimy covering which can be composed of inorganic materials, for example, clay, alum, or other inorganic colloidal substance, or organic colloidal substance, for example, cellulosic, fibrous materials, starches, and the like, which are picked up during processing. It is not uncommon in pulp slurries which are treated for microbiological control to have in the neighborhood of from several hundred thousand to over one hundred million microorganisms per milliliter of pulp slurry or whitewater. In this regard, it is significant to note that greater than a 99% reduction in microbiological contamination can be achieved through the practice of the present invention. These results represent levels of sterility in the paper industry which heretofore were thought to be unobtainable in the commercial operation of large volume production paper mills.

While effective microbiological control of pulp slurries can be achieved through the use of excessive quantities of chlorine and other microbicides, such treatment is unsatisfactory both with regard to the cost thereof and also because excessive quantities of such microbicides in and of themselves present serious problems. For example, quantitles of chlorine which, by themselves, would be effective to provide for relative sterilization of these pulp slurries, present serious odor and corrosion problems and also manifest themselves in a loss of retention, that is, a reduced ability of the fibers to form as a mat on the wire of the sheet forming equipment.

In accordance with the present invention, effective microbiological control of pulp slurries is achieved with substantially reduced amounts of chlorine or other chlorine liberating microbicides. In this regard, it should be noted that it is possible through the practice of this invention to substantially reduce the microorganism content of pulp slurry systems to levels of relative sterility. For example, in one pulp slurry system which, prior to treatment, had a microorganism population of approximately 5,000,000 microorganisms per milliliter of water, the microorganism population was reduced to a level of less than 1,000 microorganisms per milliliter of water.

This invention achieves these advantageous results through the use of chlorine or a chlorine liberating microbicide in conjunction with a water soluble anionic surfactant, preferably the sulfonated naphthalenic surfactants, particularly those having polyoxyalkyl substituents such as, for example, formaldehyde-condensed sulfonated naphthalene. In particular, an effective microbiological control of pulp slurries is achieved by the use of chlorine in amounts ranging from approximately 0.1 to 5 pounds of chlorine (or chlorine equivalent) per ton of stock (finished paper product after drying) in conjunction with from approximately 0.005 to 2.5 pounds of these anionic surfactants per ton of stock. Accordingly, it will be appreciated that the present process for microbiological control of pulp slurries, achieved through the conjoint use of these materials, is not due to the cumulative microbicidal properties of each of these materials. On the contrary, it will be readily apparent to those skilled in this art that these heretofore unobtainable levels of sterilization of pulp slurries with the amounts of chlorine or chlorine liberating microbicides employed with these anionic surfactants represent a surprising and synergistic result.

While the present invention is specifically directed to the control of microbiological slimes, a further advantageous result which occurs from the practice thereof involves the simultaneous control of chemical slimes. This control of chemical slime is believed to occur partly by reason of direct action of the chlorine or chlorine liberating microbicide on the chemical slimes and partly because the level of microbiological control is so effective as to operate to reduce the chemical slimes from forming.

It is, therefore, an important object of the present invention to provide an improved process for the microbiological control and sterilization of the wet end process of a paper making installation including the beaters, stock system and sheet forming equipment.

Another object of the present invention is to provide a novel combination of microbiological control agents, which combination effectively controls the microbiological population with concentrations of chlorine or chlorine liberating microbicides which are but a small fraction of the concentrations heretofore believed necessary in order to achieve similar results when such microbicides were used alone.

Another object of the present invention is the provision of highly efficient machine drainage conditions, decreased shutdown time, and substantial elimination of paper breaks due to the presence of microbiological contamination and chemical slimes.

Another object of the present invention is to provide a process for the microbiological control and sterilization of the wet end process of a paper making installation whereby paper and paperboard products of improved quality can be produced.

Another object of the present invention is to provide a method for the microbiological control of pulp slurries in the wet end process of a paper making installation by controlling microbiological growth to achieve relative sterilization thereof in a conventional paper making machine, which method involves the conjoint use of chlorine (preferably gaseous chlorine) or chlorine liberating microbicides, such as, for example, chlorine dioxide, hypochlorous acid, chlorine water, calcium hypochlorite, the alkali metal hypochlorites such as sodium hypochlorite, and the like in conjunction with a water soluble, anionic surfactant, preferably the sulfonated naphthalenic surfactants such as, for example, formaldehyde-condensed sulfonated naphthalene.

Another object of the present invention is to provide a method for the microbiological control of pulp slurries in the wet process of a paper making installation which permits the relative sterilization of the system and in which the level of chlorine or chlorine equivalent present at the sheet forming machine (the Fourdrinier or cylinder machine) is negligible.

These and other objects of the present invention will be apparent from the following detailed description thereof taken in conjunction with the drawing which schematically outlines an illustrative flow chart showing a typical pulp and paper processing operation.

As previously set forth, the method of this invention comprises cooperatively combining a special promoter with chlorine or a chlorine liberating microbicide in a pulp slurry which is present in the wet end process of a conventional paper making installation, that is, in the beaters, stock system and the sheet forming machines.

The special promoter of this invention is an anionic surfactant having high efiiciency as a dispersing agent. Sulfonated naphthalenic surfactants, particularly those having polyoxyalkyl substituents such as the formaldehydecondensed sulfonated naphthalene, are especially useful. The sodium salt of the sulfonated naphthalenic surfac tants are particularly preferred and are commercially available. Examples of highly satisfactory formaldehydecondensed naphthalene sulfonates which are presently commercially available are Blancol N (T.M. GAF Corporation), Darvan No. 1 (T.M. Vanderbilt Chemical Corporation), Syntan NNC (T.M. Tenneco Chemicals, Inc., Berkshire Color Division), Tamol L, Tamol N and Tamol SN (T.M. Rohm & Haas Company) and Daxad ll (Polymers and Chemical Division, W. R. Grace & Co.). The concentrations of the special promoters as expressed herein refer to the concentration of the active ingredient, e.g., the naphthalene sulfonate, and it is to be understood that the various commercially available preparations are not necessarily 100% active ingredients. Tamol N and Tamol SN are tray dried, and spray dried solids, respectively, reportedly having greater than and 93%, respectively, active sulfonated naphthalene. Tamol L on the other hand, is a nonfoaming aqueous solution reportedly having about 47% surfactant solids. Thus, for example, as expressed herein, addition of the promoter at the rate of one pound per ton of stock requires the addition of two pounds of a commercially available material which contains only 50% naphthalene sulfonate.

The microbicides which, in accordance with the present invention, are contemplated to be used in conjunction with the special promoter include chlorine and the chlorine liberating microbicides. Gaseous chlorine is preferred, however, chlorine dioxide, chlorine water, hypochlorous acid, calcium hypochlorite, the alkali metal hypochlorites such as sodium hypochlorite, and the like, can be advantageously used.

In general, effective microbiological control of the pulp slurries being treated is achieved with the use of chlorine in amounts ranging from approximately 0.1 to 5 pounds thereof (or an equivalent amount of chlorine liberating microbicide) per ton of dry stock in conjunction with approximately 0.005 to 2.5 pounds of the special promoter per ton of dry stock. It should be noted, however, that the amounts of special promoter set forth above, as well as the amounts of microbicide are those amounts required to achieve full utilization of the present invention and that amounts in excess thereof can be utilized if desired. In this regard, since substantially increased amounts of special promoter could be tolerated without adverse elfect in the system, the amount thereof contemplated by the present invention can be otherwise defined as an amount which is at least 0.005 pounds per ton of dry stock.

It will be appreciated from the illustrative examples set forth below that, in accordance with this invention, addition of the special promoter of this invention dramatically and, in fact, synergistically, enhances the effectiveness of the microbicide, as compared to the result achieved with an equal amount of unpromoted chlorine or chlorine liberating microbicide. As a result, paper process systems previously operating out of microbiological control even though chlorine was used in amounts close to the maximum which could be tolerated were, through the practice of this invention, maintained under microbiological control at chlorine levels which were but a small fraction of the level previously used, with less than satisfactory results. For example, equivalent microbicidal efficiency has been achieved, as a consequence of the presence of the special promoter of this invention, at microbicide addition levels which range from one-fifth to onetwentieth of that required in the system when the special promoter is not provided.

Referring to the figure, a flow chart showing a typical paper processing operation is illustrated. As shown, raw stock is charged to the heaters. This raw stock can consist of pulp produced at the plant site from conventional pulp source materials such as wood chips, salvaged paper, broke streams, wet lap, and the like. Wet lap systems tend to have severe microbiological problems and are particularly benefited by the method of this invention.

In the beater, the raw stock is admixed with large quantities of water. After distribution through stock chests, machine chests, and head boxes, or their equivalents, the very dilute pulp slurry, containing approximately 0.5% solids, is supplied to a sheet forming machine, for example, a Fourdrinier machine, cylinder machine, or other paper making apparatus. A large amount of water passes through the wire and, typically is recycled as so-called whitewater. The thus formed sheet of pulp, having a high water content, is then subsequently dried. Various additional treatments, for example, the addition of sizing, polishing, and the like can be provided at various stages during the drying process. The relatively dry sheet is then further processed by cutting, stacking, or the like.

The microbiological contamination of the pulp-paper process system has many sources, for example, the incoming raw pulp, waste paper, the makeup water, and the atmosphere. Due to the extreme dilution of the process stream at the sheet forming machine, it is imperative that the process water be recovered and recycled to the extent feasible. Consequently, microorganisms are repeatedly being washed off pulp solids to add to the contamination of the recycled water.

While the present invention is specifically concerned with the treatment of pulp slurries in the wet end process, it will be appreciated that each of the basic constituents employed in this process can be separately introduced at difl'erent locations.

An important aspect, however, of the present invention is that the special promoter should be fully dispersed through the body of slurry being treated prior to addition of the chlorine or chlorine liberating microbicide. Preferably, complete dispersion of the special promoter can be achieved by the addition thereof to the suction side of a pump in a process line of the wet end process located upstream of the location wherein the chlorine is added.

Chlorine addition to the slurry in accordance with the present invention is made below the liquid surface level. Preferably, chlorine gas is introduced in the pulp slurry being treated adjacent the bottom of the vessel containing such slurry. In this regard, particularly advantageous results with the present invention are achieved through the use of a portable chlorinating system of the type described in US. Letters Patent No. 3,220,430 and marketed by the Capitol Controls Company of Colmar, Pa.

The following examples are set forth for purposes of further illustrating the present invention and are not to be construed as a limitation thereon.

EXAMPLE 1 The improvement of this invention was utilized in a linerboard mill which utilized mixed newspaper repulp. This mill utilized six vats, one vat for each of the top and bottom liners and four vats for the filler. Pulp from all six vats was fed to conventional cylinder machines and the webs produced by the machines were laminated almost immediately after leaving the cylinder to form the multiply liner board. Thus, it will be appreciated that the bulk of the liner board system referred to immediately above utilized unbleached stock which traditionally is characterized by heavy microbiological contamination. The microbiological contamination of the pulp in the filler stock and machine system of this plant was extremely severe. Prior to the application of the process of this invention, the system was contaminated due to the absence of effective microbiological control to the extent that black slimy deposits were visible throughout the filler stock and machine system. This contamination was so severe that an operator could literally scoop out large quantities of black silime from the filler vats with his hands. Chlorination was being used at a level which was the maximum level permissible because of corrosion and other undesirable consequences of higher chlorine levels in the particular paper-making system, i.e., at a level of two pounds per ton of stock. Nonetheless, all filler rolls and occasionally liner rolls had to be removed and cleaned due to deposits virtually every week and substantial paper losses resulted from streaking in the top line due to microbiological contamination. Plate counts prior to the trial employment of this invention, e.g., those encountered when chlorine alone was fed at the rate of approximately two pounds of chlorine per ton of finished paper ran in the vicinity of fifty million to one hundred million microorganisms per milliliter of water.

In accordance with the present invention, the equipment was initially cleaned and approximately one-half pound of promoter per ton of dry stock fed directly into the process stream immediately before the filler machine chest, and chlorine was fed directly into the filler machine chest. The promoter utilized was the formaldehyde-condensed naphthalene sulfonate salt (sodium salt) which is commercially available as Tamol L. In the particular plant conditions, the promoter was substantially admixed with the stock prior to the application of chlorine into the machine chest. A second chlorine addition at the cylinder machine itself in the vat level was provided, but the total chlorine dosage used was far less than that used before, being approximately one pound per ton of dry stock. After initiation of the improvement of this invention, virtual sterilization was achieved in that the plate counts were reduced better than 99%, decreasing to less than 20,000 microorganisms per milliliter of both the pulp slurry and whitewater. Maintenance down time was sharply decreased and cleaner felts provided more efficient drainage. Losses of paper due to bacteriological damage was virtually eliminated and the paper produced exhibited no blow holes" or dirty streaks. Most significantly, production went from 30 tons per day to 100 tons per day (the rate capacity of this mill was tons per twenty-four hours).

EXAMPLE 2 In another paper mill using four Fourdrinier paper machines, all white paper and some colored construction paper (which starts out as all white) was produced. Hence, only bleached pulp was used and less severe microbiological contamination would be expected. However, prior to the initiation of the improvement of this invention, the plant encountered much ditficulty in keeping the Fourdrinier machine clean. Substantial fluctuations in plate counts were encountered, even though the plant was using a chlorophenate microbicide. This microbicide was being fed at various stages in the machine system and in the stock further back in the system as well as directly to the machine.

In accordance with this invention, formaldehyde-condensed naphthalene sulfonate was added to the hydropulper (heaters) at the rate of about one-half pound per ton of dry stock. Chlorine gas was added into each of the stock chests by means of a portable chlorinating system marketed by the Capitol Controls Company of Colmar, Pa., and at the rate of about one-quarter of a pound per ton of dry stock to about one-half pound per ton of dry stock. The microbiological population in the system was reduced to a level generally considered as sterile and benefits similar to those described in Example 1 were experienced. The costs of the synergistic additive system of the present invention, as a result of the decreased concentrations required, was reduced to approximately onefifth of the cost of the relatively ineifective system previously used.

EXAMPLE 3 In a series of laboratory tests, unbleached stock was taken from a machine chest and subjected to a series of individual tests to check for microbiological control using chlorine alone, i.e., without the promoter which would be added in accordance with this invention. In this series of tests, unpromoted chlorine was added in incrementally increased levels equivalents to from onehalf pound per ton of dry stock (in multiples of onehalf pound per ton) up to fifteen pounds per ton of dry stock. In this series of tests, sterilization was not achieved until those tests using fifteen pounds chlorine per ton of dry pulp were added. Taking another portion of the same stock and subjecting a series of samples to chlorine in accordance with the improvement of this invention showed that far less chlorine was required in order to achieve sterilization. -In this series of tests, the same stock was utilized and in an initial sample of the series, chlorine was added at the rate of one-half pound per ton in the presence of the promoter (Tamol L) which was present in an amount sufficient to provide a formaldehyde-condensed naphthalene sulfonate content equivalent to 0.05 pound of dry stock. In subsequent tests, each conducted with the same amount of Tamol L, the chlorine levels were respectively incrementally increased one-half pound per ton of dry stock. Relative sterilization was achieved at the chlorine addition level of three pounds per ton. Thus, in accordance with this invention, the addition of chlorine at the rate of three pounds per ton of dry stock in the presence of the special promoter was found to be equivalent to fifteen pounds per ton of dry stock of unpromoted chlorine.

EXAMPLE 4 In another series of laboratory tests, Kraft process pulp slurry containing 6% solids was taken from the stock storage chest of a paper mill and subjected to a series of individual tests to check for microbiological control using chlorine alone and chlorine in conjunction with the special promoter in accordance with the present invention. In this series of tests, unpromoted chlorine was added in incrementally increased levels and bacterial counts made thereon. Also, incrementally increased amounts of chlorine were similarly added to identical samples which contained 0.025 pounds per ton of stock of Tamol L (equivalent to approximately 0.0125 pounds of formaldehyde-condensed sulfonated naphthalene). Set forth below are Table 1 showing the data with unpromoted chlorine and Table 2 showing the data obtained with chlorine and the special promoter.

TABLE 1 Lbs. of chlorine Bacteria per ten per ml. of s no (dry basis) additive 1 'INTC 1 l TN'IC 2 l TNTC 4 1 TNTC 8 0 l6 0 1 TNT O =too numerous to count.

l TNTC=too numerous to count.

The bacterial count on the raw pulp made on a plate at 1 to 10,000 dilution was 132 using Tryptone Glucose Extract Agar which indicated the presence of 1,320,000 bacteria per milliliter.

Similarly, in each of the above tests, plate counts were made using Tryptone Glucose Extract Agar on pulp diluted on the ratio of 1 part to 1,000 parts of sterile water.

It will be noted from the above data that actual sterility was not achieved with unpromoted chlorine until 8 pounds of chlorine per ton of stock was used. Sterility, however, with chlorine used in conjunction with only 0.0125 pounds per ton of stock of formaldehydecondensed sulfonated naphthalene was achieved with as little as two pounds of chlorine per ton of stock. Similarly, it will be noted that Samples I and K, respectively,

represent situations of relative sterility in that 87% and 97% reductions in microbiological contamination were obtained. Sample L, of course, represents an instance of 100% reduction in microbiological contamination through the practice of the present invention with the same amount of microbicide as was used in sample C wherein the bacteria count after such treatment was not substantially reduced.

It will be appreciated from the above examples that the improvement of this invention provides a highly effective method of controlling or substantially elimimating the microbiological population in pulp slurries contained in the wet end process of a paper making process with substantially reduced levels of chlorine or chlorine liberating microbicide. Furthermore, the improvement of this invention is not limited to the use with cylinder machines, Fourdrinier machines, or any other specific paper making machines, such as, for example, Verta-Forma machines and the like. In the mills in which the improvement of this invention has been practiced, it has been observed that the felts remain at a high level of efiiciency since microbiological occulsion and plugging thereof is substantially eliminated. Moreover, reduced shut down time, increased efficiency of the equipment and elimination of paper loss due to microbiological damage, all cooperate to provide greatly increased production in paper mills which employ the present invention.

In the foregoing specification, the preferred embodiment of the present invention has been described in detail together with variations and modifications with respect thereto. It will be appreciated, however, that modifications and variations may be made therefrom by those skilled in the arts without departing from the spirit and scope of this invention. Accordingly, only such limitations as are indicated in the appended claims should be imposed thereon.

I claim:

1. A method of controlling the microbiological population of pulp slurries contained in the wet end process of a paper making installation, comprising the steps of: adding at least approximately 0.005 pounds per ton of dry stock of a water soluble sulfonated naphthalenic surfactant to a body of pulp slurry, thoroughly mixing said sulfonated naphthalenic surfactant in said body of slurry, and then admixing with said slurry a chlorine liberating microbicide in an amount equivalent to from approximately 0.1 to 5 pounds of chlorine per ton of dry stock.

2. The method of claim 1 wherein said sulfonated naphthalenic surfactant is substantially completely water soluble and non-foaming.

3. The method of claim 1 wherein said surfactant is an alkali metal salt of a polyoxylalkylene-substituted naphthalene sulfonate.

4. The method of claim 1 wherein said surfactant is a formaldehyde-condensed naphthalene sult'onate alkali metal salt.

5. The method of claim 1 wherein said microbicide is gaseous chlorine.

6. The method of claim 1 wherein said microbicide is selected from the group consisting of chlorine dioxide, hypochlorous acid, chlorine water, calcium hypochlorite, and the alkali metal hypochlorites.

7. A method of controlling the microbiological population of pulp slurries contained in the wet end process of a paper making installation, comprising the steps of: adding from approximately 0.005 to 2.5 pounds per ton of dry stock of a water soluble sulfonated naphthalenic surfactant to a body of pulp slurry, thoroughly mixing said sulfonated naphthalenic surfactant in said body of slurry, and then admixing with said slurry a chlorine liberating microbicide in an amount equivalent to from approximately 0.1 to 5 pounds of chlorine per ton of dry stock.

8. The method of claim 7 wherein said surfactant is an alkali metal salt of a polyoxylalkylene-substituted naphthalene sulfonate.

9. The method of claim 7 wherein said surfactant is a formaldehyde-condensed naphthalene sulfonated alkali metal salt.

10. The method of claim 9 wherein said microbicide is gaseous chlorine.

11. The method of claim 9 wherein said microbicide is selected from the group consisting of chlorine dioxide, hypochlorous acid, chlorine water, calcium hypochlorite, and the alkali metal hypochlorites.

References Cited UNITED STATES PATENTS 1,737,330 11/1929 Pattillo 162161 2,186,134 1/1940 Chapman 162-161 2,922,736 1/ 1960 Spalding 162161 OTHER REFEREN CES The Mechanism of Pitch Dispersion by Formaldehyde- Naphthalene Sulphonic Aicd Condensation Products, Poschmann, pp. T1 10 to H-114, Pulp & Paper Magazine 10 of Canada, April 1959.

Pulp & Paper Manufacture, McGraw-Hill (1955), v. 4, pp. 596-601.

S. LEON BASHORE, Primary Examiner 15 A. DANDREA, 1a., Assistant Examiner US. Cl. X.R. 162-Digest 4 

